Jayson Williams turned 34 yesterday as the sister of a limo driver slain in the hoopster’s New Jersey mansion charged that her brother would be alive if the ex-Nets star had acted quickly.

“He bled to death. If he had gotten help at first, he might have been saved. He was lying there bleeding to death,” claimed Andrea Adams, the sister of victim Costas “Gus” Christofi.

“I’m hurt. I wish that something could have been done. I just want to know the truth, that’s all,” she said.

Christofi, 55, was shot in the chest and killed by a single 12-gauge shotgun blast shortly before 3 a.m. on Valentine’s Day as he and other guests were being given a tour of Williams’ Alexandria Township mansion.

Acting Hunterdon County Prosecutor Steven Lember said Christofi bled to death from the blast, which traveled through his body and exited his lower back.

Cops said the house tour began at 2:30 a.m., and at 2:54 a.m., Williams’ adopted brother, Victor Santiago, called 911 to say someone had committed suicide in the mansion.

Christofi was pronounced dead at 3:28 a.m.

“His shoulder was blown off, his rib cage was blown out, his hip was blown off, but his heart was still pumping blood,” said Adams, who owns the Red Tower 3 restaurant in Somerville, N.J.

“No one will ever get me to believe it’s a suicide.”

Her son, Chris, said, “They flipped the story a couple of times. What could they be hiding? If there was a dozen people there, somebody knows.”